TGR5 receptor is a G-protein-coupled receptor that has been identified as a cell-surface receptor that is responsive to bile acids (BAs). The primary structure of TGR5 and its responsiveness to bile acids has been found to be highly conserved in TGR5 among human, bovine, rabbit, rat, and mouse, and thus suggests that TGR5 has important physiological functions. TGR5 has been found to be widely distributed in not only lymphoid tissues but also in other tissues. High levels of TGR5 mRNA have been detected in placenta, spleen, and monocytes/macrophages. Bile acids have been shown to induce internalization of the TGR5 fusion protein from the cell membrane to the cytoplasm. Kawamata et al. 2003, J. Bio. Chem., 278, 9435. TGR5 has been found to be identical to hGPCR19 reported by Takeda et al. 2002, FEBS Lett. 520, 97-101.
TGR5 is associated with the intracellular accumulation of cAMP, that is widely expressed in diverse cell types. While the activation of this membrane receptor in macrophages decreases pro-inflammatory cytokine production, (Kawamata, Y.; Fujii, R.; Hosoya, M.; Harada, M.; Yoshida, H.; Miwa, M.; Fukusumi, S.; Habata, Y.; Itoh, T.; Shintani, Y.; Hinuma, S.; Fujisawa, Y.; Fujino, M., A G protein-coupled receptor responsive to bile acids. J. Biol. Chem. 2003, 278, 9435-9440) the stimulation of TGR5 by BAs in adipocytes and myocytes enhances energy expenditure (Watanabe, M.; Houten, S. M.; Mataki, C.; Christoffolete, M. A.; Kim, B. W.; Sato, H.; Messaddeq, N.; Harney, J. W.; Ezaki, O.; Kodama, T.; Schoonjans, K.; Bianco, A. C.; Auwerx, J., Bile acids induce energy expenditure by promoting intracellular thyroid hormone activation. Nature. 2006, 439, 484-489). This latter effect involves the cAMP-dependent induction of type 2 iodothyronine deiodinase (D2), which by, locally converting T4 into T3, gives rise to increased thyroid hormone activity. Consistent with the role of TGR5 in the control of energy metabolism, female TGR5 knock-out mice show a significant fat accumulation with body weight gain when challenged with a high fat diet, indicating that the lack of TGR5 decreases energy expenditure and elicits obesity (Maruyama, T.; Tanaka, K.; Suzuki, J.; Miyoshi, H.; Harada, N.; Nakamura, T.; Miyamoto, Y.; Kanatani, A.; Tamai, Y., Targeted disruption of G protein-coupled bile acid receptor 1 (Gpbarl/MBar) in mice. J. Endocrinol. 2006, 191, 197-205). In addition and in line with the involvement of TGR5 in energy homeostasis, bile acid activation of the membrane receptor has also been reported to promote the production of glucagon-like peptide 1 (GLP-1) in murine enteroendocrine cell lines (Katsuma, S.; Hirasawa, A.; Tsujimoto, G., Bile acids promote glucagon-like peptide-1 secretion through TGR5 in a murine enteroendocrine cell line STC-1. Biochem. Biophys. Res. Commun. 2005, 329, 386-390). On the basis of all the above observations, TGR5 is an attractive target for the treatment of metabolic diseases e.g., obesity, diabetes (type I and type II), dyslipidemia, non-alcoholic steatohepatitis (NASH), and the metabolic syndrome.
Few examples of TGR5 agonists have been so far described in literature. Recently, 23-alkyl-substituted and 6,23-alkyl-disubstituted derivatives of chenodeoxycholic acid, such as the 6α-ethyl-23(S)-methyl-chenodeoxycholic acid shown below, have been reported as potent and selective agonists of TGR5 (Pellicciari, R.; Sato, H.; Gioiello, A.; Costantino, G.; Macchiarulo, A.; Sadeghpour, B. M.; Giorgi, G.; Schoonjans, K.; Auwerx, J., Nongenomic actions of bile acids. Synthesis and preliminary characterization of 23- and 6,23-alkyl-substituted bile acid derivatives as selective modulators for the g-protein coupled receptor TGR5. J. Med. Chem. 2007, 50, 4265-4268).

In particular, methylation at the C23—(S) position of natural BAs confers a marked selectivity to TGR5 over FXR (farnesoid X receptor) activation, whereas the 6α-alkyl substitution increases the potency at both receptors. Other TGR5 agonists include 6-methyl-2-oxo-4-thiophen-2-yl-1,2,3,4-tetrahydro-pyrimidine-5-carboxylic acid benzyl ester (WO004067008, Takeda Chemical Industries LTD, Japan, 2004) and oleanoic acid (Sato, H.; Genet, C.; Strehle, A.; Thomas, C.; Lobstein, A.; Wagner, A.; Mioskowski, C.; Auwerx, J.; Saladin, R., Anti-hyperglycemic activity of a TGR5 agonist isolated from Olea europaea. Biochem. and Biophys. Res. Commun. 2007, 362, 793-798; Ito, F.; Hinuma, K.; Kanzaki, N.; Mild, T.; Kawamata, Y.; Oi, S.; Tawaeaishi, T.; Ishichi, Y.; Hirohashi, M. Preparation of aromatic ring-fused cyclic compounds as TGR5 receptor agonists. PN: WO2004067008, 2004. More recently, the first synthesis of enantiomeric chenodeoxycholic acid (CDCA) and lithocholic acid (LCA) has allowed to assess the specificity of the interaction of natural BAs to TGR5 (Katona, B. W.; Cummins, C. L.; Ferguson, A. D.; Li, T.; Schmidt, D. R.; Mangelsdorf, D. J.; Covey, D. F., Synthesis, Characterization, and Receptor Interaction Profiles of Enantiomeric Bile Acids. J. Med. Chem. 2007, 50, 6048-6058).
While these chemical tools have provided for the first time a pharmacological differentiation of genomic versus nongenomic effects of BAs, some of them also allowed to draw a first structure-activity relationship study where the presence of an accessory binding pocket in TGR5 plays a pivotal role in determining ligand selectivity (Pellicciari, R.; Sato, H.; Gioiello, A.; Costantino, G.; Macchiarulo, A.; Sadeghpour, B. M.; Giorgi, G.; Schoonjans, K.; Auwerx, J., Nongenomic actions of bile acids. Synthesis and preliminary characterization of 23- and 6,23-alkyl-substituted bile acid derivatives as selective modulators for the g-protein coupled receptor TGR5. J. Med. Chem. 2007, 50, 4265-4268). In this context, the availability of more potent and selective TGR5 modulators is necessary to further identify additional features affecting receptor activation and characterize the physiological and pharmacological actions of this receptor.
There is a need for the development of TGR5 modulators for the treatment and prevention of disease. The present invention has identified compounds that are chenodeoxycholic acid analogues which have a substituent at the C-16 position as well as methods of using these compounds to treat disease.